The goal of this research proposal is to elucidate mechanisms whereby DNA lesions created by environmental agents are fixed into genetic lesions. The environmental agents studied include X-rays, gamma-rays, ultraviolet light, microwaves and a number of chemical carcinogens, benzo(a)pyrene, aflatoxin B1, acetylaminoflourine and safrole. The specific aims of the proposal are: 1) To determine the site of DNA sequence, to determine the relative frequencies of the different types of damage, and to determine the effect of the nucleotide sequence on the site of the damage. 2) To determine the effect of purified DNA repair enzymes on a variety of DNA lesions. Enzymes purified from bacterial and eukaryotic organisms will be used. DNA templates of defined sequence that have been modified by environmental agents will be used as substrates for DNA and RNA polymerases, and endo- and exonucleases. 3) To identify and characterize new enzymatic repair activities in human cells. DNA substrates of defined sequence modified by environmental agents will be used to identify such activities. Protein purification procedures will be applied in order to characterize the enzymes involved. 4) To identify specific enzymatic defects in cells derived from patients with genetic defects that involve faulty DNA repair such as xeroderma pigmentosum, ataxia telangiectasia, retinoblastoma, Franconi anemia and Hutchison-Gilford progeria.